1. Field of the Invention
The present invention relates to an optical memory device with optical waveguide fitted therein and to a method for fabricating such device, and more particularly relates to a method and an apparatus for lamination with a filmy member that is useful in fabricating such an optical memory device.
2. Description of the Related Art
One technique recently proposed in the art comprises introducing light into a flat (card-size) waveguide device that has a pattern formed therein for predetermined light scattering to reconstruct the intended image in an area outside the waveguide device (see, for example, IEEE Photon. Technol. Lett., Vol. 9, pp. 958-960, July 1997).
Concretely, FIG. 18 is to schematically show one example of a card-size slab waveguide device 100 that comprises a core layer 101 and two cladding layers (first and second cladding layers) 102 disposed on both sides (both faces) of the core layer 101 to put it between them. In this, the refractive index and the thickness of the core layer 101 are specifically so controlled that the core layer functions as an optical waveguide. When a fine concave and convex pattern is formed in the interface between the core layer 101 and the cladding layer 102 and when light (incident ray, reference beam, laser ray) is introduced into the core layer (waveguide) 101 via a lens 103, as in FIG. 18, then a part of the light having entered the device scatters at the concave and convex pattern, and the scattered light goes out through the cladding layer 102 as shown by the arrows in FIG. 18.
Accordingly, when the parameters of light scattering intensity and phase for reconstructing a specific image at a predetermined distance from the face of the waveguide device 101 are computed, and when a fine concave and convex pattern (for information and for information recording) is formed in the core layer 101 in accordance with the thus-computed data, then a desired image can be reconstructed in any desired area outside the waveguide device. To that effect, therefore, the core layer 101 in this device functions as an information-recording layer.
In addition, for example, when a CCD image-receiving unit 104 capable of receiving the scattered light having gone out of the waveguide device is disposed in the predetermined site and when the reconstructed image is digitized into a two-dimensional digital pattern signal (for example, into a light/dark binary pattern, or into a brightness (gray scale-based multi-level pattern), then the reconstructed image may be processed and analyzed in any desired manner with an existing digital image processor (not shown).
FIG. 19 is to schematically show another example of a conventional optical memory device. This comprises a stacked structure of multiple cladding layers 102 and core layers 101 that are alternately laminated to form multiple waveguide layers (recording layers) 101. In this, the light having scattered at a certain waveguide layer 101 shall cross the other waveguide layers 101. In general, since the refractive index difference between the core layer 101 and the cladding layer 102 is extremely small, the light having once scattered at a certain waveguide layer 101 re-scatters little in the concave and convex pattern formed in the other waveguide layers 101, and therefore the reconstructed image is disordered little. Accordingly, in the illustrated device, a large number of images and patterns can be reconstructed in proportion of the number of the stacked layers.
This means that the waveguide device 100 can be used as an optical memory device (for recording media such as ROM), of which the capacity is proportional to the number of the stacked layers of the device. In theory, the optical memory device 100 may have a capacity of about 1 Gigabyte or so per one layer, and it is said that about up to 100 layers may be stacked up in the device. Given that situation, the waveguide device of the type is considered as a hopeful device in the future for mass-storage ROM for moving image recording.
Some other proposals have been made for improving the device. For example, the core layer and the cladding layer of the device are made of resin so as to facilitate the concave and convex patterning on the resin layers. This realizes easy and inexpensive fabrication of optical memory devices having a limited volume, but having a larger capacity for increased mass storage of information therein (for example, as in Japanese Patent Application Nos. 11-131512 and 11-131513).
Now back to FIG. 18. In a case where the information recorded in the optical memory device 100 is reconstructed, an incident ray (incident laser ray) is led into the core layer 101, as shown in FIG. 18. If the cross width of the incident laser ray (incident cross width, or that is, the width of the reference beam irradiation area in the cross direction) is too narrow, only a part of the information area where the concave and convex pattern is formed receives the incident laser ray but the other part could not, and therefore, only a part of the information recorded in the information area could be reconstructed. Accordingly, the cross width of the incident laser ray must be broader than the width of the information area.
On the other hand, if the vertical width of the incident laser ray (incident vertical width, or that is, the width of the reference beam irradiation area in the vertical direction) is broad (namely, if the incident laser ray is thick in the vertical direction), the neighboring multiple core layers shall receive the incident laser ray at the same time. Accordingly, the vertical width of the incident laser ray must be as narrow as possible so that it does not cover the neighboring core layers. Therefore, in general, the spot form of the incident laser ray is long oval, which is long in the lateral direction and is as narrow as possible in the vertical direction
In conventional optical memory devices, the width of the information area is relatively narrow, and therefore, even when the device (especially the core layer therein) is warped or bent, it does not cause any serious problem in reconstructing the information recorded in the device. However, the recent tendency in the art is toward the demand for broadening the information area in optical memory devices in order to increase the quantity of information to be recorded in the devices, and, as a result, the width of the information are a in which the concave and convex pattern is formed is being broadened so as to satisfy the requirement of increasing the quantity of information to be recorded in optical memory devices.
If the width of the information area is broadened as in the above, the optical memory device (especially the core layer therein) shall naturally face the problem that it is readily warped or bent, as compared with the conventional devices where the width of the information area is narrow. As a result, the information recorded in the device having a broad information area is difficult to reconstruct.
Specifically, when the optical memory device (especially the core layer therein) is warped or bent, the entire information area where the concave and convex pattern is formed therein could not receive the incident laser ray all at a time even though the cross width of the incident laser ray is satisfactorily broad. In such a case, only a part of the information area receives the incident laser ray but the other part thereof could not, therefore resulting in image reconstruction failure.
In particular, when the information recorded in an optical memory device is reconstructed, the vertical width of the incident laser ray to be applied to the device is made narrow so that the incident laser ray does not reach the neighboring core layers of the device, as so mentioned hereinabove. Therefore, if the optical memory device (especially the core layer therein) is warped or bent, it will be more difficult to make the incident laser ray reach the entire information area of the device all at a time, and if so, the possibility of image reconstruction failure will increase.
The present invention has been made in consideration of the problems noted above, and its object is to provide an optical memory device which is so designed that the entire information area thereof can receive the reference beam applied thereto all at a time for correct image reconstruction.
In the optical memory device 100 mentioned above, it is desired to increase as much as possible the number of layers to be stacked therein for increasing the recording capacity of the device (that is, for increasing the quantity of information to be recorded in the device).
However, increasing the number of layers to be stacked makes it more difficult to reduce the inclination of the individual core layers 101 in the optical memory device 100 being fabricated. As so mentioned hereinabove, the vertical width of the incident laser ray for the device is made as narrow as possible and the form of the ray is long oval. Therefore, if the inclination of the core layers in the optical memory device 100 increases, it becomes difficult to make the entire region of one core layer 101 where the convex and concave pattern is formed (information area, information recording area) receive the incident ray (reference beam) all at a time through the end of the device 100. This means that every information recorded in one core layer 101 of the optical memory device 100 could not be reconstructed all at a time. Accordingly, it is necessary to increase the number of the layers to be stacked in the device while the inclination of each core layer 101 is reduced as much as possible.
On the other hand, when the information recorded in the multi-layered optical memory device 100 is reconstructed, the optical memory device 100 is fitted to a drive (information-reconstructing device for optical memory devices), and a flat incident ray (reference beam, such as laser ray) is led into the device 100 through its end. In that case, if the irradiation conditions of the incident ray (e.g., the irradiation position, irradiation angle, focal length, inclination of reference beam) are not good, the core layer 101 of the device 100 could receive only a part of the incident ray, and if so, the reconstructed image will be dark (its brightness will be low) and only a part of the recorded information could be reconstructed to give a defective image.
To solve the problem, it is a matter of great importance to improve the alignment accuracy of the incident ray relative to the end of the optical memory device 100. Specifically, when the information recorded in the multi-layered optical memory device 100 is reconstructed to give an intended image, it is a matter of great importance to accurately control the alignment, the angle and the inclination of the incident ray output side of the drive (e.g., the laser ray head) so that the irradiation conditions of the incident ray (e.g., the focal length, irradiation position, irradiation angle, inclination of reference beam) could be optimized relative to the optical memory device 100 fitted to the predetermined position in side the drive.
In general, for appropriately controlling the irradiation conditions of the incident ray (reference beam) (e.g., the focal length, irradiation position, irradiation angle, inclination the incident ray) relative to the optical memory device 100, the alignment, the angle and the inclination of the incident ray (from laser source or through lens) must be suitably controlled relative to the optical memory device 100. The alignment control includes, for example,  less than 1 greater than  vertical alignment control (Z-directional alignment control),  less than 2 greater than  spacing alignment control (Y-directional alignment controlxe2x80x94alignment control between the optical memory device 100 and the light source, or alignment control in the direction parallel to the incident ray-running direction),  less than 3 greater than  horizontal alignment control (X-directional alignment controlxe2x80x94alignment control in the direction perpendicular to the incident ray-running direction),  less than 4 greater than  elevation angle control (angle control, alignment control for rotation direction),  less than 5 greater than  vertical inclination control, and  less than 6 greater than  horizontal inclination control, as shown by the corresponding circled numbers in FIG. 18. For controlling the alignment, the angle and the inclination of the incident ray, the laser source and the lens system may be moved together. For simplified description herein, however, only the lens 103 is shown in FIG. 18.
However, if the inclination xcex8 to the vertical direction of the incident ray is controlled for every core layer 101 in every reading operation, the controlling operation is complicated and troublesome, and the reading operation will be difficult to automate. For example, in case where the incident ray is first moved in the vertical direction (Z-direction) so that a part of the incident ray may reach the core layer 101 and thereafter the incident ray is rotated to thereby control its inclination xcex8 in the vertical direction so that the entire incident ray may reach the core layer 101 which is for information reconstruction, if the rotation center for the incident ray rotation is not positioned in the center of that core layer 101 for information reconstruction (both in the center in the thickness direction and in the center in the cross direction), the incident ray irradiation area will be off the core layer 101 when the incident ray is rotated.
In such a case, the incident ray must be again moved in the vertical direction for vertical alignment control and then it must be rotated for the inclination xcex8 control in the vertical direction. This means that the inclination xcex8 control in the vertical direction of the incident ray requires the repeated operation of controlling the vertical alignment of the incident ray and controlling the vertical inclination xcex8 of the incident ray to thereby control the vertical alignment of the incident ray so that the thus-controlled incident ray is not off the core layer. Controlling the vertical inclination xcex8 of the incident ray for every core layer 101 of a multilayer device is complicated and troublesome, and after all, reading automation from the device is difficult to attain.
In controlling the vertical inclination xcex8 of the incident ray in the above-mentioned case, the rotation center must be all the time positioned in the center of the core layer 101 which is for information construction. For this, for example, it is necessary to detect the rotation center and to move that core layer 101 so that the center of the layer 101 is to be the rotation center. However, the apparatus for this is too much complicated and is therefore not realistic.
The present invention has been made in consideration of the problems noted above, and its object is to provide an optical memory device which is so designed that the reference beam applied thereto can reach the entire information area of every core layer to thereby correctly and accurately reconstruct the information recorded therein, not requiring any operation of controlling the incident ray inclination xcex8 for every one of the stacked core layers, and to provide a method for fabricating the device. Another object of the invention is to provide a method and an apparatus for lamination with a filmy member that are useful in fabricating such an optical memory device.
Still another object of the invention is to provide an optical memory device which is so designed that the information recorded therein can be correctly and surely reconstructed by simple control in reading the information, not requiring any complicated reading device constitution and which is therefore suitable to reading automation, and to provide a method for fabricating the device.
Still another object of the invention is to provide a method and an apparatus for lamination with a filmy member that are effective for reducing as much as possible the inclination of an increased number of stacked layers in optical memory devices for increased mass storage.
In the optical memory devices mentioned above, it is desired to increase as much as possible the number of layers to be stacked therein for increasing the recording capacity of the devices (that is, for increasing the quantity of information to be recorded in the devices).
However, the increased number of stacked layers increases the degree of warping of the optical memory devices fabricated. As so mentioned hereinabove, the vertical width of the incident laser ray for optical memory devices is made as narrow as possible and the form of the ray is long oval. Therefore, if the warping of the core layers in the optical memory devices fabricated increases, it becomes difficult to make the entire region of one core layer where the convex and concave pattern is formed (information area, information recording area) receive the incident ray (reference beam) all at a time through the end of the device. This means that every information recorded in one core layer of the optical memory device could not be reconstructed all at a time.
Accordingly, it is necessary to increase the number of the layers to be stacked in the device while the warping of each core layer is reduced as much as possible. For this, for example, a stiff substrate may be used in fabricating the optical memory device or the thickness of the substrate may be increased so as to reduce the degree of warping of the device fabricated. For example, when 100 layers are stacked up and when the thickness of one core layer is 1.8 xcexcm and that of one cladding layer is 30 xcexcm, then the resin thickness to constitute the stacked core layers and cladding layers shall amount to about 3.2 mm. In such a case, even though a stiff substrate of glass is used for preventing the stacked layers from being warped, the substrate must be thick (for example, having a thickness of at least 5 mm).
If such a stiff substrate or a thick substrate is used for preventing the stacked layers from being warped, not only the thickness of the substrate increases but also the weight of the device fabricated increases. This is unfavorable since it results in the increase in the cost of the apparatus for fabricating optical memory devices (apparatus for fabricating recording media).
In addition, even if the number of the layers to be stacked could be increased while the stacked layers are prevented from being warped according to the method as above, the increase in the number of the layers to be stacked inevitably reduces the productivity of the devices to be fabricated. For example, when 100 layers are continuously stacked up, the productivity of the devices with the stacked layers therein inevitably reduces. The problem of the productivity reduction will be more serious when the number of the layers to be stacked is increased further.
The present invention has been made in consideration of the problems noted above, and its object is to provide an optical memory device of which the advantages are that the device warps little even when the number of the layers to be stacked therein is increased so as to increase the recording capacity of the device, the information recorded in the device can be correctly and accurately reconstructed, and the productivity of the device is high.
To solve the problems as above and to attain the objects as above, the invention provides the following:
An optical memory device that comprises a core layer and a cladding layer laminated on both surfaces of the core layer, wherein at least one interface between the core layer and the cladding layer has a concave and convex pattern for information to form a waveguide and a reference beam is introduced into the core layer through the end of the waveguide for reconstructing the information recorded in the concave and convex pattern for information, and wherein the degree of bending of the core layer at the end of the information area in which the concave and convex pattern for information is formed satisfies the condition represented by the following formula:
xcex94txe2x89xa6dxe2x88x92t
in which xcex94t indicates the degree of bending of the core layer at the end of the information area,
d indicates the vertical width of the reference beam, and
t indicates the thickness of the core layer in the information area;
An optical memory device that comprises a core layer and a cladding layer laminated on both surfaces of the core layer, wherein at least one interface between the core layer and the cladding layer has a concave and convex pattern for information to form a waveguide and a reference beam is introduced into the core layer through the end of the waveguide for reconstructing the information recorded in the concave and convex pattern for information, and wherein the degree of bending, at the end of the device, of the width that corresponds to the width of the information area in which the concave and convex pattern for information is formed in the uppermost face or the lowermost face of the device satisfies the condition represented by the following formula:
xcex94txxe2x89xa6dxe2x88x92t
in which xcex94tx indicates the degree of bending, at the end of the device, of the width that corresponds to the width of the information area in the uppermost face or the lowermost face of the device,
d indicates the vertical width of the reference beam, and
t indicates the thickness of the core layer in the information area.
Preferably, the optical memory device comprises a core layer of resin and a cladding layer of resin laminated on both surfaces of the resinous core layer, and comprises at least five waveguide blocks each having a concave and convex pattern for information formed in at least one interface between the resinous core layer and the resinous cladding layer, and in which the stacked structure of the waveguide blocks is sandwiched between thin-film base layers.
Also preferably, the optical memory device comprises a core layer and a cladding layer laminated on both surfaces of the core layer and comprises at least five stacked waveguide blocks each having a concave and convex pattern for information formed in at least one interface between the core layer and the cladding layer, wherein the stacked structure of the waveguide blocks has an end through which the reference beam is introduced into the core layer for reconstructing the information recorded in the concave and convex pattern for information, and wherein the degree of inclination of the core layer at the end of the device and relative to the standard face of the information area in which the concave and convex pattern for information is formed satisfies the condition represented by the following formula:
|a|xe2x89xa6dxe2x88x92t
in which a indicates the degree of inclination of the core layer at the end of the device and relative to the standard face of the information area,
d indicates the vertical width of the reference beam, and
t indicates the thickness of the core layer in the information area.
Also preferably, the optical memory device comprises a core layer of resin and a cladding layer of resin laminated on both surfaces of the resinous core layer and comprises at least two stacked structure units, wherein each stacked structure unit comprises one or more waveguide blocks sandwiched between base layers and each waveguide block has a concave and convex pattern for information formed in at least one interface between the resinous core layer and the resinous cladding layer.
The invention also provides a method for fabricating an optical memory device by stacking a core layer and a cladding layer, which comprises a coating step of coating a base substrate with a photocurable resin to form thereon a core layer or a cladding layer, and a laminating step of laminating the core resin or the cladding resin with a transparent stamper which has a concave and convex pattern formed on its surface and which transmits light for curing the photocurable resin, by the use of a laminate roll applied to the transparent stamper, and which is characterized in that the transparent stamper is laminated onto the core resin or the cladding resin while the distance between the surface of the base substrate coated with the core resin or the cladding resin and the laminate roll is kept constant in the laminating step.
The invention further provides a method for fabricating an optical memory device by stacking a core layer and a cladding layer, which comprises a coating step of coating a base substrate with a resin to form thereon a core layer or a cladding layer, and a laminating step of laminating the core resin or the cladding resin with a resin film by the use of a laminate roll, and which is characterized in that the resin film is laminated onto the core resin or the cladding resin while the distance between the core resin or the cladding resin and the laminate roll is kept constant in the laminating step.
Preferably, the lamination method comprises a step of coating a base substrate with a resin material, and a step of laminating the resin layer with a filmy member by the use of a roll, and in which the filmy member is laminated onto the resin-coated base substrate while the distance between the resin-coated surface of the base substrate and the roll is kept constant in the laminating step.
The invention still provides an apparatus of lamination with a filmy member which is for laminating a base substrate with a filmy member via a resin layer therebetween, and which comprises a stage for mounting thereon the base substrate to be laminated with the filmy member, a laminate roll by which the filmy member is laminated onto the resin layer formed on the surface of the base substrate to be laminated with the filmy member, and an alignment controller for controlling the height of the laminate roll from the stage so that the distance between the stage and the laminate roll is not lower than a predetermined level.